PROJECT SUMMARY Prisons and jails are the de facto largest providers of mental health services in the U.S. The failure to effectively treat mental illness in this setting is associated with a host of dire outcomes: higher rates of suicide; higher rates of victimization for rape and other forms of abuse; higher rates of rules infractions and solitary confinement; and higher rates of recidivism and re-arrest after release. Thus, there is a critical need for more effective mental health treatment strategies for incarcerated individuals. There is a particular need for more targeted therapeutic approaches for individuals with post-traumatic stress disorder (PTSD). The prevalence of trauma history and PTSD are markedly higher in jail and prison populations than in the general population. In fact, the prevalence of PTSD among inmates exceeds that of military combat veterans. Despite the pressing need for PTSD treatment within the jail and prison population, there is virtually no research examining the effectiveness of empirically-supported therapies for PTSD in incarcerated individuals. Cognitive Processing Therapy (CPT) is a promising PTSD treatment for the prison setting, primarily due to its cost- and time- effectiveness in the manualized group format. In studies of non-incarcerated individuals, CPT has been found to be more effective than waitlist control and equivalent to Prolonged Exposure. Yet, there has never been a study of CPT among adult prison inmates. This R34 project will lay the groundwork for a sustained research effort to dramatically improve the treatment of PTSD in our nation's prisons. This pilot study will cover the initial project development stages: (1) Establish the feasibility of group CPT delivery in male and female prisons; (2) Obtain preliminary effectiveness estimates for reducing PTSD symptom severity; and (3) Identify putative psychological mechanisms of symptom change through pre-, mid-, and post-intervention assessments. Through a unique partnership with the State of Wisconsin Department of Corrections, we will collect and analyze data for both male and female prison inmates. Completion of these aims is a requisite initial step to implement and evaluate a promising PTSD intervention in this severely underserved and costly population. By demonstrating the feasibility and effectiveness of empirically-supported group psychotherapy in the prison setting, this program of research could ultimately help radically improve the treatment of psychiatric illness among prison inmates.